A number of rare earth-iron alloys have been developed which exhibit desirable magnetostrictive properties as described, for example, by Savage et al in U.S. Pat. No. 4,308,474 which issued Dec. 29, 1998. The alloys described therein (e.g., Tb-Dy-Fe alloys) have been found to be useful in magnetostrictive transducers, delay lines, variable frequency resonators and filters.
Another group of alloys based on rare earth-iron-boron compositions is described by Schmidt et al in U.S. Pat. No. 4,612,047 issued Sept. 16, 1986 and by Seon et al in U.S. Pat. No. 4,636,353 issued Jan. 13, 1987. The alloys (e.g., Nd-Fe-B) exhibit highly desirable magnetic properties for use as permanent magnets.
The commercialization of these rare earth-transition metal alloys has progressed to the point that relatively large quantities of rare earth-transition metal alloy scrap have been generated from the various manufacturing operations used to fabricate the alloys into suitable magnet components, electrical components and the like. The rare earth-transition metal alloy scrap generated by these fabrication operations varies considerably in form from dry, bulky relatively large scrap pieces to a fine powder or dust referred to as "swarf".
Industries that fabricate rare earth-transition metal alloys into articles of manufacture require some method to dispose of the scrap and recover the valuable rare earth material in a form amenable for reuse. In particular, a treatment process is needed that allows recovery of a rare earth metal salt (e.g., a rare earth metal fluoride) for use in the thermite reduction process (described by Schmidt et al. in U.S. Pat. No. 4,612,047) or for use in other metallothermic processes for preparing the respective rare earth metal or alloy. Moreover, a treatment method should be provided for treating iron-bearing wastes that typically will result from the rare earth recovery treatment process.
An object of the invention is to address these needs by providing a relatively low cost, wet method of treating rare earth-transition metal alloy scrap in a manner to recover the rare earth metal thereof for use in the thermite or other metallothermic reduction process for preparing the respective rare earth metal or alloy.
Another object of the invention is to provide a relatively low cost, wet method of treating transition metal (e.g., iron)-bearing waste solutions that result from the rare earth recovery treatment to recover the transition metal for reuse.